Today's integrated circuits include a vast number of devices. Smaller devices are key to enhance performance and to improve reliability. Smaller devices entail ever more difficult manufacturing techniques, combined with more reliability and reproducibility requirements. Semiconductor devices are in need of a large variety of thin films, or layers; metallic, insulating, semiconducting. Over the years many thin layer deposition techniques have been devised. Many of these are so called low pressure deposition processes, which as the name implies, carry out the deposition at pressures well below the atmospheric region. Examples of such low pressure deposition techniques are: chemical vapor deposition (CVD) including metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), atomic layer deposition (ALD), physical vapor deposition (PVD) and others. The layer thicknesses of interest can range from many microns to a few atomic layers on the semiconductor substrate undergoing processing. The deposition of these films are for diverse purposes, such as the formation of wiring structures, electrical contacts, gate electrodes, diffusion barriers, and others.
It is noted that for the sake of simplicity the discussion here is mostly for the specific case of CVD, but the scope of the invention is not limited for this particular process. During processing typically a stream of precursor gas is passed into the system for deposition onto a substrate. In case of metal deposition by MOCVD the precursor gas is comprising organometallic species containing the metal to be deposited, and deposition usually occurs after some surface chemical reactions on the substrate. For efficient manufacturing it is necessary that the deposition apparatus in repetitive operation produce films with constant physical properties (such as thickness, resistivity, crystallographic phase, surface roughness, etc.) over hundreds, or even thousands of substrates without interruption. To do so the critical deposition parameters must be kept constant. One of these parameters is the substrate temperature during deposition. The film growth rate is generally dependent upon the substrate temperature, so that any drift of the substrate temperature with repetitive reactor operation will lead to a deviation of the film properties from the desired values. For instance, in a MOCVD process, such as W deposition from W(CO)6, besides layer thickness, the resistivity, the crystallographic phase of the deposited metal, and the surface roughness will also vary if the substrate temperature changes. For this deposition process, a substrate temperature change of as little as 5% can lead to unacceptable changes in film properties.